My First Boat...Boat Term Question...
Well, it's time I buy my first boat now, after sailing for almost 6 months I'm ready to do it. I know what I'm looking to do with the boat ( cruising around the islands and long distance blue water cruising), I know I want a big sturdy and heavy keel on it.
However, I don't yet feel like I have a thorough education on some of the "boat costruction terms" and how they effect the boat in detail ie: displacement, draft, masthead vs fractional. I know what a Ketch is but I'm not sure what a Cutter is.
Also, I'd like to learn more thoroughly about the different types of keel shapes.
Can you guys help me out? And maybe give me a brief description of how each part of a boat affects the boat's handling? And perhaps point me to a good reference online on the details of a boat's construction.
K - You should spring for a copy of Nigel Calder's The Cruising Handbook. Half the book is devoted to the boat and it's systems. Very good reference guide.
While individual things affect a boat, it is how they are put together as a whole that is most important. Here's a link to a listing of "suitable" offshore boats http://www.mahina.com/cruise.html with a lengthy commentary on boat selection.
And to answer your one specific question, a cutter is a double headsail sloop.
Kac... Well congrats on making the big decision. First thing I would suggest is to search on bluewater boats here and read the already existing threads as a lot of what you ask has been discussed quite thoroughly. After that you may have more pointed questions to ask.
Here's a list of one guys take on what are "bluewater" boats worth considering which can give you some models to look at on Yachtworld.com so you can see what is appealing to you.
It is not comprehensive...and leaves out Tayana entirely (which I of course disagree with since the 37 is a classic world cruiser) but it is a starting point.
How big a boat are you considering and what is your maximum price range? Will you be single-handing or having crew? Are you looking for new, slightly used or very used? Here's a couple of very brief answers to some of your basic questions:
Masthead rig means the jib/jenny is rigged to the top of the mast vs. a fractional rig where it is rigged lower and has less sail area. Typically mainsails are bigger on fractional rigs and the mast is a bit more forward than on a masthead rig where the jib is both more powerful and harder to handle do to size.
Displacement is a measure of the weight of the water the boat displaces and tells you relatively little about the performance as a 20000 lb displacement can come from anywhere on the boat...from the masthead to the keel...but that is still how much weight the wind will have to move. Many blue-water sailors prefer heavily built high displacement boats but new materials and production techniques have some opting for lighter, more easily driven boats that are nonetheless seaworthy.
A cutter is a boat with two headsails..see my picture above of a cutter rigged ketch!
Keels go from full to cutaway forefoot to fin, to bulb to wing to centerboard. Full or cutaway forefoot keels tend to be found on heavy displacement traditional boats. They track straight and have little leeway and offer protection to the rudder and prop. They tend to be pigs for docking manoeverability and backing up. Fin keels are found on the majority of boats today as they are quicker and more manoeverable and still can provide lots of ballast to keep the boat stiff and upright. Sometimes the fins have wings on them to allow a more shallow draft and still keep the weight low but wing keels tend to get stuck harder around when you do find shallow water as we all do! Bulb keels put all the weight down deep but are generally more suceptible to damage and typically found on racer/cruisers.
Combined with these keels are either spade rudders which are fast and help manoueverability as they are a "blade on a post" but they are more prone to damage since they hang freely. Skeg hung rudders are less quick but are supported in multiple places by the hanging skeg part of the hull which also protects them.
Contruction of hulls in "fiberglass" is a huge subject since both quality of construction methods and advanced construction materials exist today. So...I will just say for now that the biggest differences people focus on are the use of "chopped spray on fiberglass" vs. hand laid up glass mat, and cored hulls (which are esstentially a sandwich of balsa or foam between two fiberglass skins). Cored hulls MAY be light, fast and strong AND may be used just above the waterline or on the entire hull. You can see the debates on this on other threads...but the big risk of cored is water intrusion between the layers and delamination as a result.
OK...go read and come back with more questions! <g>
On your list there appears an oversight as Catalina is not listed either. Must be on the same list as the Tayana. (smile)
Nauticats made the bluewater cruiser list on Cam's link . . .:)
Thank you for your answers! Especially Cam for your extensive answer. You're always answering my posts :)
I am going off to read all you suggested now.
I guess a fin keel boat is what I will be looking for. I have heard that bulb keels are prone to damage as the bolts that attacth the bulb to the keel take a lot of stress.
My price range?
I am looking to spend between $15,000 to $27,000 on a used boat.
I have found a boat the other day that I fell in love with, but I don't know what you'll think of it.
It is a 1969 Discovery 32' cruiser. Tell me what you think.
This is right in my price range and the size I'm looking for.(28 to 35 feet) The interior is also very well thought out and designed very well.
This boat isn't on that list that you gave me, I think because it is more or less a rare boat and there ain't much of them around.
Oh yeah, I love the green hull paint job too :) But I am still waiting on a reply with more detailed specs from the owner. Apparantly he's sailed it across the Pacific several times.
How many people am I looking for the boat to hold? I think it will be myself and 1 or 2 other crew members. I might single hand it for shorter trips for now :)
Kacper...I know nothing about this boat but she LOOKS seaworthy and well kept. If you proceed further with her, a couple of things would concern me.
1. The boat is built with a cored hull. I would not buy a cored hull but fine boats like Shannon use them so that is my personal predjudice. The main thing you need to worry about is that the hull is currently in good shape all over the hull with no delamination. Find a surveyor that YOU can trust if you make an offer and have it accepted.
2. Why is this boat priced so low? A couple of others are up near $30K and "yours" has a virtually new $10k+ engine in it. It may be a genuine deal but you rarely get a boat for 1/3 off the market price without something being wrong. Survey, Survey, Survey!
Anyway...other than that, I like her and think she looks ideal for your purposes and budget...hope #1 & 2 above are not issues!!
I would highly recommend Dave Gerr's book, The Nature of Boats. Great primer on design, construction, materials, etc.
These are drafts that I had written for another venue but they may help a bit:
The next topic in our ongoing discussion on selecting the ideal boat is rigs. Like most of the topics to date, there is no single universally ‘right answer’ when it comes to the topic of rigs. Boats are designed as systems and the each of the various rig types have their purpose and are best suited to particular hull types, and applications. The quality of the design is also important as a poorly designed rig of any type can make for a miserable sailing vessel that is hard on the crew and the boat alike.
Cutter and Sloop rig
These are the most common rigs being produced today. In current usage these terms are applied quite loosely as compared to their more traditional definitions. Traditionally the sloop rig was a rig with a single mast located forward of 50% of the length of the sailplan. In this traditional definition a sloop could have multiple jibs. Cutters had a rig with a single mast located 50% of the length of the sailplan or further aft, multiple headsails and in older definitions, a reefing bowsprit (a bowsprit that could be withdrawn in heavy going). Somewhere in the 1950's or 1960's there was a shift in these definitions such that a sloop only flew one headsail and a cutter had multiple headsails and mast position became irrelevant. For the sake of this discussion I assume we are discussing the modern definition of a sloop and a cutter.
Historically, when sail handling hardware was primitive and sails were far more stretchy than they are today, the smaller headsails and mainsail of a traditional cutter were easier to handle and with less sail stretch, allowed earlier cutters to be more weatherly (sail closer to the wind) than the sloops of the day. With the invention of lower stretch sailcloth and geared winches, cutters quickly lost their earlier advantage.
Today sloops are generally closer winded and easier to handle. Their smaller jibs and larger mainsail sailplan are easier to power up and down. Without a jibstay to drag the Genoa across, sloops are generally easier to tack. With less hardware sloops are less expensive to build.
Sloops come in a couple varieties, masthead and fractional. In a masthead rig the forestay and jib originates at the masthead. In a fractional rig, the forestay originated some fraction of the mast height down from the masthead. Historically, sloops were traditionally fractionally rigged. Fractional rigs tend to give the most drive per square foot of sail area. Their smaller jibs are easier to tack and they reef down to a snug masthead rig. Today they are often proportioned so that they do not need overlapping headsails, making them even easier to sail. One of the major advantages of a fractional rigs is the ability when combined with a flexible mast, is the ability to use the backstay to control mast bend. Increasing backstay tension does a lot of things on a fractional rig: it tensions the forestay flattening the jib, and induces mast bend, which flattens the mainsail and opens the leech of the sail. This allows quick depowering as the wind increases and allows a fractional rig to sail in a wider wind speed range than masthead rig without reefing, although arguably requiring a bit more sail trimming skills.
While fractional rigs used to require running backstays, better materials and design approaches have pretty much eliminated the need for running backstays. That said, fractional rigs intended for offshore use, will often have running backstays that are only rigged in heavy weather once the mainsail has been reefed. The geometry of these running backstays typically allows the boat to be tacked without tacking the running backstays.
Masthead rigs came into popularity in the 1950's primarily in response to racing rating rules that under-penalized jibs and spinnakers and so promoted bigger headsails. Masthead sloops tend to be simpler rigs to build and adjust. They tend to be more dependent on large headsails and so are harder to tack and also require a larger headsail inventory if performance is important. Mast bend is harder to control and so bigger masthead rigs will often have a babystay that can be tensioned to induce mast bend in the same way as a fractional rig does. Dragging a Genoa over the babystay makes tacking a bit more difficult and slower. While roller furling allows a wider wind range for a given Genoa, there is a real limit (typically cited 10% to 15%) to how much a Genoa can be roller furled and still maintain a safely flat shape.
Cutters, which had pretty much dropped out of popularity during a period from the end of WWII until the early 1970's, came back into popularity with a vengeance in the early 1970's as an offshore cruising rig. In theory, the presence of multiple jibs allows the forestaysail to be dropped or completely furled, and when combined with a reefed mainsail, and the full staysail, results in a very compact heavy weather rig (similar to the proportions of a fractional rigged sloop with a reef in the mainsail). As a result the cutter rig is often cited as the ideal offshore rig. While that is the theory, it rarely works out that the staysail is properly proportioned, (either too small for normal sailing needs and for the lower end of the high wind range (say 20-30 knots) or too large for higher windspeeds) and of a sail cloth that makes sense as a heavy weather sail or which is too heavy for day to day sailing in more moderate conditions. Also when these sails are proportioned small enough to be used as heavy weather sails, these rigs will often develop a lot of weather helm when being sailed in winds that are too slow to use a double reefed mainsail. Like fractional rigs, cutter rigs intended for offshore use, will often have running backstays that are only rigged in heavy weather once the mainsail has been reefed. Unlike the fractional rig, the geometry of these running backstays typically requires that the running backstays be tacked whenever the boat is tacked.
Cutters make a less successful rig for coastal sailing. Generally cutters tend to have snug rigs that depend on larger Genoas for light air performance. Tacking these large Genoas through the narrow slot between the jibstay and forestay is a much harder operation than tacking a sloop. As a result many of today's cutters have a removable jibstay that can be rigged in heavier winds. This somewhat reduces the advantage of a cutter rig (i.e. having a permanently rigged and ready to fly small, heavy weather jib).
Cutters these days generally do not point as close to the wind as similar sized sloops. Because of the need to keep the slots of both headsails open enough to permit good airflow, the headsails on a cutter cannot be sheeted as tightly as the jib on a sloop without choking off the airflow in the slot. Since cutters are generally associated with the less efficient underbodies that are typical of offshore boats this is less of a problem that it might sound. Cutters also give away some performance on deep broad reaches and when heading downwind because the Genoa acts in the bad air of the staysail.
Yawls and Ketches:
As I said at the start of this discussion, boats are systems and when it comes to one size fits all answers, there is no single right answer when it comes to yawls and ketches either. A Yawl is a rig with two masts and the after mast (the mast that is further aft or further back in the boat) is aft of the rudder. A ketch is a rig with two masts, the after mast is forward of the rudder. Either rig can have either a single jib or multiple jibs. When a Yawl or a Ketch has multiple jibs it is referred to a Yawl or a Ketch with multiple headsails. It is considered lubberly to refer to that rig as a 'cutter ketch' or 'cutter Yawl'.
I lump yawls and ketches together here because the share many similar characteristics. Ketches, in one form or another, have been around for a very long time. In the days before winches, light weight- low stretch sail cloth, high strength- low stretch line, and low friction blocks, breaking a rig into a lot of smaller sails made sense. It made it easier to manhandle the sails and make adjustments. Stretch was minimized so the sails powered up less in a gust and although multiple small sails are less efficient, the hulls were so inefficient that the loss of sail efficiency did not hurt much. Multiple masts, along with bowsprits and boomkins, allowed boats to have more sail area that would be spread out closer to the water. In a time of stone internal ballasting, and high drag in relatinship to stability, this was important as it maximized the amount of drive while minimizing heeling. In theory, multiple masts meant more luff length and more luff length meant more drive forces to windward. But multiple masts also meant more weight and much more drag. There are also issues of down draft interference, meaning that one sail is operating in the disturbed and turbulent air of the sails in front of it, which also greatly reduces the efficiency of multi mast rigs.
Yawls really came into being as race rule beaters. They are first seen in the 1920's as a rule beater under the Universal and International rules. They continued to be popular under the CCA rule as well. Under these rules, the sail area of jibs and mizzens were pretty much ignored in the rating. This popularized the masthead rig and the yawl.
There was a basis for not measuring the sail area of a yawl under these rules. On a yawl going to windward, the mizzenmast and sail generally actually produce more drag than they do drive. This is because the mizzen is sailing in really turbulent air and has to be over trimmed to keep from luffing which can effectively act as an airbrake. This is slightly less of the case on a ketch where the size of the mizzen is large enough to provide a larger percentage of the drive.
Downwind mizzens also are a problem. In this case the mizzen is forcing the main or foresail to operate in their bad air and so again the mizzen is not adding as much to the speed of the boat as they are taking away. BUT in the predominantly reaching races that were typical of offshore races of that era they offered a number of advantages. First of all on a reach the sails are not acting in the slipstream of each other and so each contributes a fair amount of drive for the drag produced. Also with the advent of lightweight low stretch sailcloths, mizzen staysails, which are great reaching sails, came into widespread usage in racing. Here again a ketch has the advantage of having a taller mizzen and so can fly a bigger mizzen staysail.
It might be helpful to compare yawl and ketch rigs to sloops. The broad generalities are that for a given sail area a sloop rig will generate a greater drive for the amount of drag generated pretty much on all points of sail. That means that a sloop will be faster or will require less sail area to go the same speed. Sloops are particularly better than Multi spar rigs such as Yawls and Ketches on a beat or on a run. A sloop rig would tend to be taller for a given sail area. This means it would be better in lighter air but it potentially might heel more, or need to be depowered or reefed sooner as the breeze picks up.
Sloops work best on boats with reasonably modern underbodies. Both are more efficient and so can point higher and make less leeway.
Ketch and Yawl rigs work best with heavier boats with less efficient underbodies such as full keels and deeply Vee'd hull forms. These hull forms often need a lot more drive and the hull is the limiting factor in how fast or how close-winded the boat will be. The yawl or ketch rig's lack of windward ability is less of a liability when placed on a hull that similarly lacks windward ability. Also, the ability of a ketch or yawl to carry more sail with less heeling moment also makes it a natural for a heavier hull form which often has comparatively little stability when compared to the amount of drive required to make a heavy boat move.
Much is made of the ketch or yawl's ability to be balanced to help with self-steering, to hove to, or the ability to simply sail under Jib and mizzen in a blow. This is one aspect that a traditional ketch or yawl has over a traditional sloop. It is not so true of modern sloops. Modern (especially fractional) sloops can be easily depowered and that reduces the need to reef. With modern slab reefing gear, reefing is far more easily accomplished than dropping the mainsail to the deck on a yawl or ketch. In a properly designed sloop balance is just not all that hard to achieve.
The performance of all three rigs, both on broad reaches and in lighter air, can be improved by the ability to carry kites of different types.
In terms of comfort at sea, ketch and yawl rigs push the weight of the spars closer to the ends of the boat which can increase pitch angles, albeit, while perhaps slowing pitching rates. The taller rigs of a sloop tend to increase roll angles while slowing roll rates.
Then there are structural issues. It is often difficult to properly stay a ketch or yawl rig as the mainmast backstay often need to be routed around the mizzen and the forward load component of the mizzen if often taken by the top of the mainmast. It is also often difficult to get proper aft staying on the mizzen of a ketch or yawl as well. These structural issues are particularly pronounced on Yawls where the mast is so far aft in the boat that on a traditional boat it is hard to get adequate staying base widths.
Many of the early fiberglass yawls were very poorly engineered. I heard the story of how the Bristol 40 became a yawl. It seems that Clint Pearson (who owned Bristol) had started to build a Bristol 40 sloop on order for a particular customer. As the boat was nearing completion the prospective owner bailed out leaving Mr. Pearson with bit of a problem. Almost at the same time came an enquiry about the availability of a Bristol 40 yawl for prompt delivery for a different person. Without hesitation the potential buyer was told that they happened to have a yawl that was almost finished and would be available in a few weeks. Bristol was building a 24 foot Corsair and they took a mast and rigging from a Corsair and used that for the mizzen. A block of wood was glassed onto the hull for a mast step and a hole cut in the deck for the mast to go through and Voila- the Bristol 40 yawl. Several more were built like that and they quickly proved problematic. Eventually the design was engineered to solve the problems that occurred on the first few yawls.
You often hear people say that yawls and ketches are simpler rigs to handle. I am not clear why that is assumed to be so as there are more sails to trim and more interaction between the individual sails. As on a sloop, you start trimming from the forward most sail moving aft. Also as on a sloop, fine tuning, small adjustments are made moving forward again to reduce downdraft interference between the sails. Sailed with the same degree of precision, a ketches and yawls require more fine tunning than a sloop but on the whole about the same amount of fine tuning as a cutter.
Anyway, in conclusion, if you are interested in sailing performance or ease of handling, a sloop rig makes more sense. To me the only justification for the yawl rig today is solely romantic charm, or a sense of history. I do not mean this to be a put down to those who love historic rigs, but for sheer sailing ability a yawl or ketch is a relic of another time, or an obsolete racing rule. Still, if you live in an area that is typically windier and you like traditional boats, then a ketch or yawl is an interesting albeit complicated rig.
Schooners, more than any of the other fore and aft rigs, are really a series of rigs. They vary from the modern unstayed cat schooners (like the Freedom 39), to Fenger's experiments with wishbone schooners, to the traditional two-masted gaff schooners, to the early 19th century square topsail schooners, to the knockabout and the staysail schooners of the late 1930's, to the 4, 5 and 6 masted cargo schooners of the early 20th century. Each of these has distinct advantages and disadvantages.
By definition a schooner is a rig with two or more masts with the after mast(s) equal or taller than the forward mast(s).
Schooners, in one form or another, have been around for a very long time. Like most multi-masted rigs, they evolved in the days when breaking a rig into a lot of smaller sails made sense. Multi-masted rigs resulted in a rig with a greater number of smaller low aspect ratio sails. These proportionately smaller sails reduced stretch within the individual sails, made it easier to manhandle the sails and make sail shape adjustments. This was a time before winches, light weight- low stretch sailcloth, high strength- low stretch line, and low friction blocks. These proportionately smaller sails powered up less in a gust. While multiple small sails are less efficient, the hulls of the era were so inefficient that this loss of sail efficiency did not hurt much.
Multiple masts, along with bowsprits and boomkins, allowed boats to have more sail area that could be spread out closer to the water. In a time when stone internal ballasting was the norm, this was important as it maximized the amount of drive while minimizing heeling moments. Multiple masts meant more a little more luff length and more luff length meant greater drive force on a reach or beat. But multiple masts also meant more weight aloft and much more aerodynamic drag increasing heel some and greatly reducing the relative efficiency of the sails. Multi mast rigs also have the issue of downdraft interference, meaning that each sail is operating in the disturbed and turbulent air of the sails upwind of it, which also greatly reduces the efficiency of multi mast rigs. .
Schooners are best suited for burdensome vessels with comparatively little stability. They are best used in sailing venues where they predominantly will be reaching between 30 degrees above a beam reach to approximately 50 degrees below a beam reach. Because of the geometry and inherently high drag of the schooner rig they are not very good rigs upwind or down. Upwind, the large amount of aerodynamic drag from the spars and, in stayed rigs, rigging, coupled with the typically low aspect ratio sails typical of a schooner rig, and the down-drafting problems of a multi-masted rig, results in very poor windward performance. When compared with Yawls, which can drop their mizzen when beating without much consequence, a Schooners primary drive sail(s) are acting in the wind shadow of the entire rig.
Probably the highest upwind efficiency is achieved in schooners with lug foresails. On a schooner, lug foresails are not actually 'lug rigged'. In the case or a schooner, the term 'lug foresail' means a gaff foresail (not a jib) that foresail that over laps the mainsail in much the same manner as a Genoa over laps the mast on a modern rig. This rig was common in American working craft in the 19th century partially because there was no boom to deal with on the working deck. It was used on such boats as the yacht America's original rig, Tancook Whalers and on many Atlantic coast pilot boats. Lug foresails need to be tacked around the mast in much the same manner as a Genoa is today.
Downwind the problem of downdraft interference is a major problem as well. The large mainsail again tends to block the air on the sails forward of it and schooners really do not have a tall forward mast on which to fly a meaningful spinnaker. While there are all kinds of kites that can be flown from a schooner, and early working schooners often carried square sails on their foremasts, most of these patches really come into their own on a reach.
I once had a great conversation with Olin Stephens about schooners. Someone had asked why the schooner rig had died out. In the course of the conversation it was pretty much concluded that as hull forms became increasingly efficient, the schooner rig could not keep up. Great efforts at all kinds of rig improvements were tried but in the end the inherent limitations of the schooner rig was ill matched to the improved hull forms of the early 20th century.
Today, traditional schooners are wonderful to look at relics of a bygone age. Traditional forms of the schooner rig are complicated rigs that are expensive to build and maintain. They generally lack the strength of staying of a more modern rig. They are limited in their ability to beat to windward, hove to, or go dead downwind. They require greater skill to sail well and are pretty labor intensive to sail in shifting conditions. Still there is nothing like the romance of gaff topsail schooner with a bone in her teeth.
This month’s topic looks at appemdages. In principle Appendages keep a boat from making leeway and help a boat steer. They come in many shapes and sizes. Keels are supposed to be a fixed appendage and centerboards generically are moveable appendages that occur on the centerline but centerboards are just one kind of moveable appendage. In more detail:
The earliest form of a keel was simply the backbone of the boat extending through the bottom planking. (Like a Viking ship) That works OK with running and reaching sails but when you try to point toward the wind you slip side wards at great speed. As sails and rigs were invented that allowed boats to point toward the wind the keel was extended below the boat either by planking the hull down to a deeper backbone or by adding dead wood (solid timber below the backbone. A planked down keel permitted the space between the planking to be filled with heavy material (originally stone), which served as ballast keeping the boat from heeling. After a while it was discovered that there were advantages to bolting a high-density cast metal ballast to the outside of the deadwood and interior ballast dropped out of fashion.
These earliest keels pretty much ran from the point of entry at the bow, to the aft most point of exit at the stern. Those are full keels in the fullest sense of the word.
They have some advantages; they theoretically form a long straight plane, which keeps a boat on course better (greater directional or longitudinal stability). If you run aground they spread out the load over a larger area reducing the likelihood of damage. Once really planted they keep the boat from tipping over fore and aft. They are easier to haul and work on. You can spread out the ballast over a longer distance and so they can be shallower for the same stability. You have a greater length to bolt on ballast so it is a theoretically sturdier and simpler connection.
They have some disadvantages; a larger portion of the keel operates near the surface and near the intersection of the hull and keel, which are both turbulent zones. They also have comparatively small leading edges, and the leading edge is the primary generator of lift preventing sideslip. Because of that they need a lot more surface area to generate the same lift. Surface area equates to drag so they need more sail area to achieve the same speed. Long keels tend to be less efficient in terms of lift to drag for other reasons as well. As a boat makes leeway water slips off of the high-pressure side of the keel to the low-pressure side of the keel and creates a turbulent swirl know as a tip vortex. This is drawn behind the boat creating drag in a number of ways. The longer the keel, the bigger the vortex, the greater the drag. So they need more sail area again to overcome this drag. To stand up to this greater sail area the boat needs more ballast and a stronger structure, which is why long keelboats are often heavier, as well. (Of course, then the spiral starts again as more sail area is needed to overcome that additional weight as well. It is the classic weight breeding more weight design cycle) Full keels tend to be much less maneuverable.
By the classic definition of a fin keel any keel whose bottom is less than 50% of the length of the boat is a fin keel. Fin keels came into being in an effort to reduce drag. Cut away the forefoot or rake the stem, as well as, move the rudderpost forward and rake it sharply and pretty soon you have a fin keel. Today we assume that fin keels mean a separated rudder (skeg hung or spade) but in fact early fin keels had the rudder attached in a worst of all worlds situation. They offer all of the disadvantages of both full and fin keels, but with none of the virtues. Unknowing or unscrupulous brokers will often refer to boats with fin (or near fin) keels as full keel if they have an attached rudder.
Fin keels with separate rudders seem to be the most commonly produced keel form in the US these days. (I could be wrong, there is a resurgence of full keels these days)
Fin keels have some advantages as well. They have less drag as explained above so they typically make less leeway and go faster. You can get the ballast down lower so in theory they are more stable for their weight. They are more maneuverable. They take better advantage of the high efficiency of modern sail plans and materials.
They have some disadvantages as well, many of these have been offset or worked around by modern technology but at some level they are still accurate critiques. They have less directional stability than long keel boats so the tend to wander more under sail. Since directional stability is also a product of the dynamic balance between the sail plan and underbody, in practice they may actually hold a course as well as a full keel. In general though you can expect to make more course adjustments with a fin keel. It is sometimes argued that the lower helm loads requires less energy to make these corrections so a fin keel may also require less energy to maintain course. This I think is a product of the individual boat and could lead to a debate harder to prove than the number of angels that can dance on the head of a pin.
Fin keels are harder to engineer to withstand a hard grounding and when aground they are more likely to flop over on their bow or stern. (Although in 37 years of sailing, I have never heard of anyone actually experiencing this.) Fins typically have deeper draft. They are easier to pivot around and get off in a simple grounding.
A shoal keel is just a keel that is not as deep as a deep keel. Today the term seems to be applied mostly to shallow fin keels. Shallow full keels seem to be referred to as shoal draft boats. A shallow fin is a tough animal to classify. Like a fin keel with an attached rudder, I really think it has few of the advantages of either a deep fin or a full keel and has many of the worst traits of both full and fin. This can be partially offset by combining a shallow fin with a centerboard, which is a neat set up for shoal draft cruising.
A lot can be done to improve a shallow fin. One way is to add a bulb. A bulb is a cast metal ballast attachment added to the bottom of the keel. They concentrate the ballast lower providing greater stability and sail carrying ability than a simple shallow keel. Traditionally bulbs were torpedo or teardrop shaped. They have been re-contoured to provide some hydrodynamic properties. Recalling the discussion on tip vortex from above. Shallow keels need to be longer horizontally than a deeper fin in order to get enough area to prevent leeway. This means that a shallow longer fin would generate more tip vortex and more drag than a deeper keel. The bulb creates a surface to turn the water aft and prevent it from slipping over the tip of the keel thereby reducing tip vortex. This does not come free since a bulb increases frontal area and surface area.
Wing keels are a specialized type of bulb keel. Instead of a torpedo shaped bulb there are small lead wings more or less perpendicular to the keel. These concentrate weight lower like a bulb and properly designed they also are very efficient in reducing tip vortex. There has been some discussion that wings increase the effective span of the keel when heeled over but this does not seem to be born out in tank testing of the short wings currently being used in production sailboats. Not all wings are created equal. They potentially offer a lot of advantages, but they are heavily dependent on the quality of the design and I really think that many wing designs are not really working to their potential.
Then there is the whole grounding issue. In 2002, the Naval Academy did a study of keel types and grounding. They found that the popular perception that wing keels are harder to free is accurate. In their study, wing keels were extremely harder to free. Straight fins were much easier to free, especially when heeled, and the easiest keel to free was the bulb keel.
Keels that are not really keels:
Swing keels are ballasted centerboards and drop keels are ballasted daggerboards that are ballasted beyond what it takes to submerge themselves. They are really forms of centerboards. More on these in the discussion on centerboards.
Keels that are keels that move.
I said in the introduction that keels do not move. That used to be true. We now have canting keels, which can be pivoted from side to side. They are best designed to be light fins with heavy bulbs that can be canted to windward increasing the effectiveness of the righting aspects of the keel. Just one problem, a keel canted to windward losses efficiency to prevent leeway so they really need other foils to keep leeway in check. I frankly do not like the idea of a canting keel. I think canting keels are too complex and potentially problematic.
Centerboards are appendages that can be raised and lowered on or near the centerline of the boat. They can rotate up into a trunk or rotate below the boat. Daggerboards are a type of centerboard that raises vertically or near vertically in a trunk. Swing keels are a type of rotating centerboard that actually contains a substantial portion of the boat’s ballast. They may be housed in a trunk like a Tartan 27 or 34 or hung below the boat like a Catalina 22. In the case of the Tartan 27 or 34 they are more frequently referred to as a Keel/ Centerboard (abbreviated k/cb). A swing keel is intended to act as a fin keel when lowered and allow some sailing in the partially raised position. My biggest problem with swing keels is that most do not have a positive lock down. In an extreme knockdown they can slam up into the hull greatly reducing the boat’s stability. This is a pretty rare occurrence and usually requires big wave action combined with a lot of wind, but I have experienced it out in the Atlantic.
A drop keel is a daggerboard that actually contains a substantial portion of the boat’s ballast. These are easier to lock down but can be more easily damaged in a grounding. They generally have better shape than a swing keel and can be more robust, but not always are.
Other appendages: (besides the rudders)
Bilge keels (or twin keels for our English friends) are a pair of keels (usually fins these days) that emerge on either side of the boat and angle out. They offer some advantages. If you let the boat dry out the boat can stand on the two keels and wait the next tide. There are dubious theories about increased efficiency since one is vertical like a good leeway resisting foil and one is canted like a good stability inducing foil. With computer modeling there has been greater success in approaching that theory on large bilge keel boats. While bilge keels do allow shallow draft though, they extremely difficult to free once aground since having the two keels on the ground prevents heeling the boat to get free. In practice bilge keels have enormous wetted surface creating a lot of drag at lower speeds, and produce two very large tip vortexes creating a lot of drag at speed.
Keel Centerboards are a wonderful choice for coastal and offshore cruising. Properly designed they offer nearly the performance of a fin keel, and yet permit access to shallower venues. They can be partially raised to precisely control the center of lateral resistance and therefore offers the ability to have a very neutral helm and great tracking in a wide range of conditions. Properly constructed they have proven to have a long service life. Keel-centerboard boats really proved themselves offshore during the late 1950’s and into 1960’s.They fell out of popularity with the advent of the wing keel in the early 1980’s. The downside is that they are a little harder to maintain, and because the ballast is closer to the center of buoyancy they require more ballast and so end up requiring a higher overall displacement, a higher ballast to displacement ratio, or are more tender, or some combination of the three.
Bilge boards (for the scow guys), are a pair of centerboards that angle out of each side of the boat. They work well on scows but I’ve never been able to really figure out scows anyway. Seriously, You raise the windward board and lower the Leeward one on each tack and because they are close to vertical they can be small and efficient. I still don’t get the scow thing.
Last but not least- Leeboards. Leeboards are foils that are bolted to the side of the hull like on Dutch Jachts and Herreshoff Meadowlarks. Phil Bolger’s sharpies use them a lot as well. They have some advantages but they drive me nuts. They are vulnerable in docking and ideally are raised and lowered on each tack also. Some are raised to be hinged feather so they do not need to be raised.
So that’s about it. The final is tomorrow- multiple choice and essay.
|All times are GMT -4. The time now is 03:05 AM.|
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2015, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012